Film for flexible packaging is used for a multitude of applications. For a stretch hood, as described in WO2006/076917 A1, the hood is formed from a biaxially oriented tubular film having a seam. In this application, the seam provides flexibility in sizing the hood but reinforcement for demanding packaging applications is missing. In case of baling forage or hay, EP0923866 A1 presents a stretch film provided with a pest deterrent, which increases the cost and the weight of the product considerably.
Several cases are known in the art where the reinforcing phase is located in a specific layer, thus, creating laminate structures in the film. In US2005/0175805 A1 a plurality of fibres are dispersed between two thermoplastic layers made during a blown process. This fibre-reinforced film, which is mainly formed into a bag, consists of an inner layer of randomly dispersed fibres, thus, discontinuities in fibre volume fraction per film unit length appear. This produces uneven reinforcement.
Co-extruded reinforced film for packaging has received increased attention over the last few years. U.S. Pat. No. 4,536,362 discloses a longitudinally ribbed plastic film by extrusion through a special designed die-head. Similarly, in WO2005/021240 A1 the longitudinal co-extruded thicker regions are aimed to strengthen the film. In these documents where inexpensive reinforced packaging film is targeted, uncontrollable thickness fluctuation and thus, property variation, appears. Additionally, the overall reinforcement is provided by the increased cross-section of the thicker section and not by its inherent enhanced properties.
To this end, it should be noted that reinforced extendible systems are already available on the market provided with longitudinal reinforcing strips which are fastened to a film to increase its mechanical strength in the longitudinal direction even if its weight is kept low. It is evident that such reinforced systems of the known type need a coupling between the film to be reinforced and the reinforcing strips which have to be applied thereto. This adds additional processing to the usual operations of production and thus, additional cost. The same holds for embodiments where perforated reinforced packaging film is exploited for wrapping packed products, which need aeration.
In certain embodiments where thin flexible packaging with enhanced tensile strength in the machine direction is needed, the prior art has proposed either single wide reinforcing strips or folded/overlapped reinforcing elements. These, however, cause a prominent weight increase and debonding effects.
The use of stretch films of polyethylene for packaging or unitizing goods is known. In heavy applications depending on the weight and size of goods, films with different characteristics (strength, thickness, tack, slip) are exploited.
For a film producer the major cost comes from polyethylene raw-material. It is therefore understood that the packaging cost increases in proportion to the thickness. Therefore, it is useful to decrease the thickness of the films for packaging to reduce their production cost.
Furthermore, the waste volume and weight obtained by packaging or unitizing goods is also dependent on the thickness of the film. Thus, reducing the thickness leads to less waste volume and weight.
An important feature of reinforced thermoplastic films is the strength of the link between base film and reinforcing element. Strengthening of this link/bond can be achieved by coupling agents or process steps to ensure the stability.
The object of the present invention is to overcome the problems mentioned above.